boost/graph/connected_components.hpp

0001 //
0002 //=======================================================================
0003 // Copyright 1997-2001 University of Notre Dame.
0004 // Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek
0005 //
0006 // Distributed under the Boost Software License, Version 1.0. (See
0007 // accompanying file LICENSE_1_0.txt or copy at
0008 // http://www.boost.org/LICENSE_1_0.txt)
0009 //=======================================================================
0010 //
0011 #ifndef BOOST_GRAPH_CONNECTED_COMPONENTS_HPP
0012 #define BOOST_GRAPH_CONNECTED_COMPONENTS_HPP
0013
0014 #include <boost/config.hpp>
0015 #include <boost/graph/depth_first_search.hpp>
0016 #include <boost/graph/properties.hpp>
0017 #include <boost/graph/graph_concepts.hpp>
0018 #include <boost/graph/overloading.hpp>
0019 #include <boost/graph/detail/mpi_include.hpp>
0020 #include <boost/static_assert.hpp>
0021 #include <boost/concept/assert.hpp>
0022
0023 namespace boost
0024 {
0025
0026 namespace detail
0027 {
0028
0029     // This visitor is used both in the connected_components algorithm
0030     // and in the kosaraju strong components algorithm during the
0031     // second DFS traversal.
0032     template < class ComponentsMap >
0033     class components_recorder : public dfs_visitor<>
0034     {
0035         typedef typename property_traits< ComponentsMap >::value_type comp_type;
0036
0037     public:
0038         components_recorder(ComponentsMap c, comp_type& c_count)
0039         : m_component(c), m_count(c_count)
0040         {
0041         }
0042
0043         template < class Vertex, class Graph > void start_vertex(Vertex, Graph&)
0044         {
0045             if (m_count == (std::numeric_limits< comp_type >::max)())
0046                 m_count = 0; // start counting components at zero
0047             else
0048                 ++m_count;
0049         }
0050         template < class Vertex, class Graph >
0051         void discover_vertex(Vertex u, Graph&)
0052         {
0053             put(m_component, u, m_count);
0054         }
0055
0056     protected:
0057         ComponentsMap m_component;
0058         comp_type& m_count;
0059     };
0060
0061 } // namespace detail
0062
0063 // This function computes the connected components of an undirected
0064 // graph using a single application of depth first search.
0065
0066 template < class Graph, class ComponentMap, class P, class T, class R >
0067 inline typename property_traits< ComponentMap >::value_type
0068 connected_components(const Graph& g, ComponentMap c,
0069     const bgl_named_params< P, T, R >& params BOOST_GRAPH_ENABLE_IF_MODELS_PARM(
0070         Graph, vertex_list_graph_tag))
0071 {
0072     if (num_vertices(g) == 0)
0073         return 0;
0074
0075     typedef typename graph_traits< Graph >::vertex_descriptor Vertex;
0076     BOOST_CONCEPT_ASSERT((WritablePropertyMapConcept< ComponentMap, Vertex >));
0077     typedef typename boost::graph_traits< Graph >::directed_category directed;
0078     BOOST_STATIC_ASSERT((boost::is_same< directed, undirected_tag >::value));
0079
0080     typedef typename property_traits< ComponentMap >::value_type comp_type;
0081     // c_count initialized to "nil" (with nil represented by (max)())
0082     comp_type c_count((std::numeric_limits< comp_type >::max)());
0083     detail::components_recorder< ComponentMap > vis(c, c_count);
0084     depth_first_search(g, params.visitor(vis));
0085     return c_count + 1;
0086 }
0087
0088 template < class Graph, class ComponentMap >
0089 inline typename property_traits< ComponentMap >::value_type
0090 connected_components(const Graph& g,
0091     ComponentMap c BOOST_GRAPH_ENABLE_IF_MODELS_PARM(
0092         Graph, vertex_list_graph_tag))
0093 {
0094     if (num_vertices(g) == 0)
0095         return 0;
0096
0097     typedef typename graph_traits< Graph >::vertex_descriptor Vertex;
0098     BOOST_CONCEPT_ASSERT((WritablePropertyMapConcept< ComponentMap, Vertex >));
0099     // typedef typename boost::graph_traits<Graph>::directed_category directed;
0100     // BOOST_STATIC_ASSERT((boost::is_same<directed, undirected_tag>::value));
0101
0102     typedef typename property_traits< ComponentMap >::value_type comp_type;
0103     // c_count initialized to "nil" (with nil represented by (max)())
0104     comp_type c_count((std::numeric_limits< comp_type >::max)());
0105     detail::components_recorder< ComponentMap > vis(c, c_count);
0106     depth_first_search(g, visitor(vis));
0107     return c_count + 1;
0108 }
0109
0110 } // namespace boost
0111
0112 #include BOOST_GRAPH_MPI_INCLUDE(<boost/graph/distributed/connected_components.hpp>)
0113
0114 #endif // BOOST_GRAPH_CONNECTED_COMPONENTS_HPP